A specific field of application for the present invention is refiners for the manufacture of fiber—or papermaking pulp from wood chips or similar cellulosic material. Refiners of the disc-type are formed with a refining gap between the refining elements of the refining members extending in the radial direction, which gap proceeds from a central feed zone for the raw material where the centrifugal force is relatively low. The centrifugal force acting on the refining material then increases very strongly with increasing radius. In order to prolong the stay-time in the outer portion of the refining gap, the refining gap in the outer portion can be conical, with an extension at an angle in relation to the radial direction, so that only part of the centrifugal force is able to act on the refining material in the flow direction of flow within the gap. The refining gap thus consists of an inner radial zone and an outer conical zone.
The above discussion implies that the refining material in the conical zone is thrown outwardly to the refining elements located outwardly by the effect of the centrifugal force and the bars on the refining elements located inwardly. The refining material substantially contains fibrous material, but impurities in the form of sand and other abrasive materials can in certain cases follow along with the fibrous material. The aforesaid flow conditions can thus create increased wear of the bars on the refining element located outwardly. It has been found that wear primarily manifests itself on the edges of the bars on these refining elements being worn at least twice as fast as corresponding bar edges on the inwardly located refining elements. As the wear of the bars on the refining elements causes a deterioration of the quality of the worked material, the refining elements must be exchanged before their quality has become unacceptable. Furthermore, the energy consumption in the refiner increases. Every exchange of refining elements is not only expensive, but it also means that the refiner must be taken out of operation, which means loss of production.
One object of the present invention is to reduce the above problems, in that the refining elements intended for the outwardly located refining means in the conical zone has a configuration which to the greatest possible extent counteracts the wear thereof.